Method and device for cleaning a cylinder of a printing press

ABSTRACT

A method and a device for cleaning a cylinder of a printing press—in particular of a flexographic printing press—are described wherein a layer of ink to be transferred to a web substrate to be printed—such as paper, plastic film and the like—is deposited on said cylinder ( 1 ) and wherein a fluid suitable to detach impurities from the area concerned is sent onto the surface of the cylinder ( 1 ) to be cleaned and a suction is provided to remove said impurities from the cylinder surface, said cleaning fluid being vapour.

The present invention refers to a method and a device for cleaning acylinder of a printing press, particularly of a flexographic printingpress.

As is known, in a flexographic printing press there is a large-sizedcylinder, on which is passed a web of material to be printed—such aspaper, plastic or the like—and one or more plate cylinders, which takeink from an inking roll and transfer it to the web of material to beprinted.

In these printing presses, according to the material of the websubstrate to be printed, the plate cylinders tend to get dirty more orless rapidly, both with the printing ink and with particles that detachfrom the print substrate, such as dust, fibres and other foreign bodies.

It therefore becomes necessary to clean the print cylinders or platecylinders so as not to compromise the print quality.

To do this, it is normally necessary to stop the printing process, toremove the cylinder from its seat and to carry out a manual washing orcleaning thereof. All this obviously results in a considerable waste oftime.

To overcome this drawback, automatic print cylinder cleaning systemshave been proposed, which carry out washing of the cylinder periodicallywithout it being removed from its working seat and without having tostop the machine.

These systems normally consist in a carriage, which is movedlongitudinally to the plate cylinder whilst it is in rotation, so as totreat the entire surface area of the cylinder.

A cleaning device of this type is described, for example, in EP 0 742756 and comprises a cleaning or washing head moveable along the axis ofthe cylinder and able to spray onto the cylinder a mixture of compressedair and of a liquid which are previously mixed in a mixing chamberdisposed upstream of the sprayer nozzle.

Downstream of the sprayer nozzle for fluid under pressure, in thedirection of rotation of the cylinder, suction is provided to remove theimpurities detached by the fluid under pressure.

Such a solution proves somewhat complex due to the presence of themixing pre-chamber, and furthermore does not ensure drying or completeremoval of the washing liquid, residues of which can remain on thecylinder.

WO 01/54 909 describes a device for cleaning a plate cylinder, whereinthe nozzle for spraying the washing liquid onto the cylinder is disposedinside a suction chamber, downstream of which at least one suctiondrying chamber for removing the residues of washing liquid from thesurface of the cylinder is provided.

This solution also proves somewhat complex due to the fact that thesprayer nozzle must be kept inside a closed suction chamber and in anycase it does not ensure complete removal of the residues of washingliquid.

Object of the invention is to eliminate the drawbacks of already knownsystems for cleaning a print cylinder.

In particular, an object of the invention is to provide a method and adevice for cleaning a cylinder of a printing press that allow perfectcleaning of the cylinder surface to be performed without leavingresidues of the washing fluid thereon.

Another object of the invention is to provide a method and a device thatare cheap and simple to achieve.

Another object of the invention is to provide a method and a device thatcan be used both with solventless inks and with solvent-based inks andUV inks.

These and other objects are achieved with the method and the deviceaccording to the invention, which have the characteristics ofindependent claims 1 and 8, respectively.

Advantageous embodiments of the invention are apparent from thedependent claims.

Substantially, according to the invention, a jet of vapour to thesurface to be cleaned and a subsequent suction to remove the impuritiesremoved from the cylinder are provided.

Downstream of the suction there is advantageously provided a jet of airunder pressure to dry the treated surface.

The vapour sprayer nozzle is disposed inside a chamber that surrounds itand the suction chamber has an arched profile, which extends for anangle of about 180° around and in front of the sprayer nozzle.

The jet of air on the other hand is shaped as a continuous ordiscontinuous blade.

The vapour used for washing the plate cylinder is simple steam, in themost common case in which solventless inks are used for printing.

However, in the case of solvent-based or UV inks, other substances in aliquid or vapour state can be added to the steam, in particular suitablesolvents compatible with the different types of inks for removing theinks used for printing and the impurities deposited on the cylinder.

In addition to the excellent cleaning results that can be obtained withthe use of vapour, it has surprisingly been noted that said vapour doesnot cause a rise in temperature of the cylinder, which might haveadversely affected the printing process.

Further characteristics of the invention will be made clearer by thedetailed description that follows, referring to a purely exemplary andtherefore non limiting embodiment thereof, illustrated in the appendeddrawings, in which:

FIG. 1 is a diagrammatic axonometric view showing the device accordingto the invention applied to a plate cylinder;

FIG. 2 is a partial front view of the device of FIG. 1;

FIG. 3 is a section along the line A-A of FIG. 2;

FIG. 4 is a view from the right-hand side of FIG. 2, according to arrowF;

FIG. 5 is a bottom view of the cleaning head of FIG. 4;

FIG. 6 is a section along the line B-B of FIG. 4;

FIG. 7 is an exploded view of the cleaning head.

With reference to the appended figures, and in particular to FIG. 1, thenumeral 1 denotes a print cylinder or plate-carrying cylinder, whichhereunder will also be called plate cylinder, that is a cylinder onwhich the printing ink is distributed to be transferred to a substrateof web material, not shown, which is passed on a cylinder, normally of alarge size, disposed to the rear of the cylinder 1, and also not shown.

Obviously there may be more than one cylinder 1, disposed along theperiphery of the impression cylinder, according to the printing to bedone on the web substrate.

FIG. 1 shows diagrammatically a vapour supplier 2 that is a boiler forvapour generation with an accumulation tank, an aspirator 3 and acompressor 4, respectively to send the vapour and to suck and sendcompressed air, through respective pipes 5, 6, 7, in a cleaning head 8,which will be better described later.

The head 8 is supported by a plate 9, which can slide linearly along arod 10 so as to move in both directions along the axis of the cylinder1. In this manner, whilst the cylinder is rotating in the direction ofthe arrow shown thereon, the head 8 performs cleaning thereof in themanner that will be described below.

Obviously operation of the cleaning head 8 and movement thereof alongthe axis of the cylinder 1 are established according to the websubstrate to be printed and to the ink used.

Considering now the subsequent figures, it can be seen that the cleaninghead 8 comprises an upper body 11, substantially parallelepiped inshape, with suitable apertures for the passage of working fluids and alower body 12, also provided with suitable apertures and ending at thebottom in a circular cradle shape 13, such as to adapt to the surface ofthe cylinder 1 to be treated (see in particular FIGS. 3 and 7).

The two bodies 11 and 12 are joined together, after interposition of asuitably perforated gasket 14 and of centring pins 15, by means of apair of lever hooks 16, operation of which can be clearly understoodfrom the figures.

In the upper body 11 a vertical through opening 17 is provided, havingat the top a circular section 18 designed to house the end of the duct 6coming from the aspirator 3 and having at the bottom an arched profile19 with which corresponding apertures with an arched profile (20, 21),provided respectively in the gasket 14 and in the lower body 12 (FIG.7), are coupled.

The arched aperture 21 provided in the lower body 12 of the cleaninghead takes on a substantially semi-circular shape 23 at the lower face13 of said body 12 (FIG. 5).

On a side wall of the upper body 11 of the cleaning head two holes (24,25) for connecting respectively the duct 5 coming from the vapoursupplier 2 and the duct 7 coming from the compressor 4 are alsoprovided.

The hole 24, substantially horizontal, communicates with a vertical hole27, slightly inclined, in which a vapour sprayer nozzle 28 is fixed,whose end houses in a substantially cylindrical chamber 29 provided inthe lower body 12, remaining at a suitable distance from the surface ofthe cylinder 1 to be cleaned.

A corresponding substantially circular hole 30 is provided in the gasketfor passage of the nozzle 28.

The hole 25 for connecting the duct 7 of the compressor 4, formed in theupper body 11, is also substantially horizontal and communicates with asubstantially vertical hole 31 (FIG. 6) with which coincide a hole 32formed in the gasket 14 and a vertical hole 33 formed in the lower body12 (FIG. 7), which in turn communicates with a horizontal duct 34 (FIG.3) which distributes the air through a series of offset holes 35 openingonto the lower surface 13 of the lower body 12 of the cleaning head(FIG. 5) and oriented along the axis of the cylinder 1.

Having described the structure of the device according to the invention,its operation should be obvious.

Whilst the cylinder 1 rotates in the direction of the arrows shown onthe drawings, the nozzle 28, disposed in the chamber 29 with its axisslightly inclined with respect to the vertical, emits a jet of vapourinclined by about 100 with respect to the perpendicular to the surfaceof the cylinder 1, thus causing the ink residues and all otherimpurities to be detached from said surface.

These impurities are sucked downstream of the nozzle 28 through the slot23, whose semicircular shape in front of the nozzle 28 is optimal forremoving said impurities and for preventing them from being dispersedsideways.

To finish off, a jet of compressed air is sent onto the surface of thecylinder through the two series of offset holes 35, again disposeddownstream of the slot 23, to eliminate any residual moisture and toobtain a complete drying.

With the common water-based inks which are normally used in flexographicprinting of the substrate of web material, the nozzle 28 sprays steamonto the surface of the cylinder 1 to remove said inks.

If solvent-based inks or UV inks, which cannot be removed with steamalone, are used, suitable solvents—in the liquid state or also in thevapour state—that are compatible with the various types of ink are addedthereto. Glycol or ethyl acetate-based solvents mixed in water inpercentages of 30-50% are indicated as a limiting example of saidsolvents.

As stated previously, it has surprisingly been noted that the use ofvapour, contrary to what might have been thought, does not cause anyincrease in temperature of the surface of the cylinder 1 to be cleaned,whose effect on printing would have been unpredictable.

Of course, the invention is not limited to the particular embodimentdescribed herein and illustrated in the appended drawings, but numerousmodifications of detail within the reach of a person skilled in the artcan be made thereto, without thereby departing from the scope of saidinvention as defined by the claims that follow.

1. A method for cleaning a cylinder (1) of a printing press, wherein alayer of ink to be transferred to a web substrate to be printed—such aspaper, plastic film and the like—is deposited on said cylinder (1) andwherein a cleaning vapour fluid able to detach impurities from the areaconcerned is sent onto the surface of the cylinder (1) to be cleaned anda suction to remove said impurities from the cylinder surface isprovided, characterised in that said vapour is sent under pressure in aslightly inclined direction with respect to the perpendicular to thecylinder surface (1) through a nozzle (28) housed in a cavity (29) of acleaning head (8) and in that said suction takes place immediatelydownstream of the vapour jet through a slot (23) in said cleaning head,partially surrounding the nozzle (28), and placed outside said cavity(29).
 2. A method according to claim 1, characterised in that saidvapour is steam.
 3. A method according to claim 2, characterised in thatsaid steam is added with suitable solvents in the liquid or vaporousstate, compatible with the various types of ink, for removal ofsolvent-based inks or UV inks.
 4. A method according to claim 3, whereinsaid solvents are glycol or ethyl acetate based, mixed in water inpercentages of 30-50%.
 5. A method according to claim 1, characterisedin that said suction slot has a curved profile extending over an arc ofabout 180°.
 6. A method according to claim 1, characterised in thatdownstream of said suction a jet of pressurized air for drying of thecylinder is provided.
 7. A device for cleaning a cylinder of a printingpress, in particular of a flexographic printing press, comprising a head(8) mounted longitudinally moveable along the axis of the cylinder (1)and comprising a nozzle (28) for sending a washing vapour fluid onto thezone of the cylinder surface (1) to be cleaned and a suction means (23)for removal of the impurities that are detached from the cylinder (1),characterized in that said nozzle (8) is supplied with vapour underpressure by a vapour supplier (2), is housed in a cavity (29) of saidcleaning head (8) and is oriented so as to direct the jet of vapour in aslightly inclined direction with respect to the perpendicular to thecylinder surface (1) and in that said suction means (23) is a suctionslot disposed immediately downstream of the nozzle, partiallysurrounding it, outside said cavity (29).
 8. A device according to claim8, characterized in that said vapour is steam, possibly added withsuitable solvents, in the liquid or vaporous state, compatible with thevarious types of inks, for removal of solvent-based inks or UV inks. 9.A device according to claim 8, wherein said solvents are glycol or ethylacetate based, mixed in water in percentages of 30-50%.
 10. A deviceaccording to claim 8, characterized in that said suction slot (23) has acurved profile extending over an arc of about 180°.
 11. A deviceaccording to claim 8, characterized in that downstream of said suctionslot (23) said cleaning head (8) has a plurality of holes or continuousslots for delivery of a jet of air under pressure onto the cylindersurface (1).
 12. A device according to claim 8 characterized in thatsaid cleaning head (8) comprises an upper body (11) and a lower body(12), centred by means of pins (15) and fixed to each other by couplingmeans (16), said lower body (12) having at the bottom a curved surfacewhich substantially reproduces the curvature of said cylinder (1).
 13. Adevice according to claim 11, characterised in that between said upper(11) and lower (12) body of the head (8) a gasket (14) is interposed,suitably perforated to allow communication between ducts (24, 27) forfeeding vapour, ducts (25, 31) for feeding compressed air and a duct(19) for suction of air provided in said upper body 11 and correspondingopenings (29) for discharge of vapour, openings (35) for discharge ofcompressed air and openings (23) for suction of air, provided in saidlower body (12).
 14. A device according to claim 12, characterised inthat said upper body (11) of the cleaning head (8) comprises a circularupper hole (18) for connection of a tube (6) connected to an aspirator(3) and side holes (24, 25) for connection to respective tubes (5, 7)connected respectively to said vapour generator and to a compressor (4).